3*7 


UNIVERSITY  OF  CALIFORNIA  Agricultural  Experiment  Station 

College  of  agriculture  e.  j.  wickson,  acting  director 

BERKELEY,   CALIFORNIA 


CIRCULAR  No.  27 

(October,  1906.) 


Marly  Subsoils  and  the  Chlorosis  or 
Yellowing  of  Citrus  Trees. 


BY 

E.  \7.  HILGAED. 


It  was  early  ascertained  by  this  Station,  and  has  been  repeatedly 
stated  in  its  publications,  that  the  great  majority  of  California  soils, 
in  common  with  those  of  the  arid  regions  generally,  is  calcareous  in 
the  sense  of  containing  lime  enough  to  produce  all  its  advantageous 
effects.  In  the  East,  and  in  the  humid  region  generally,  these  effects 
have  very  frequently  to  be  brought  about  by  artificial  liming  or  "marl- 
ing"; an  operation  which  but  very  rarely  is  of  practical  use  in  this 
State. 

It  is  also  well  known  that  "  over  liming, "  or  the*  use  of  too  much 
lime  or  marl,  is  very  injurious  to  many  culture  plants.  The  case  in 
point  best  known  is  probably  that  of  the  phylloxera-resistant  grape- 
vine stocks  brought  to  France  from  the  Northern  United  States.  The 
soils  in  the  grape-growing  regions  of  France  are  very  commonly  marly, 
and  the  result  was  the  chlorosis,  or  yellowing  of  the  leaves,  and  general 
failure  of  the  American  stocks  on  soils  whose  lime-content  would  not 
affect  the  European  vine  injuriously  at  all.  The  latter  is  credited  with 
enduring  even  as  much  as  40  per  cent  of  lime  carbonate  in  the  soil, 
while  some  of  the  American  resistants  are  injured  by  as  little  as  5  per 
cent,  of  the  same.  Hence  the  mission,  a  number  of  years  ago,  of  Pro- 
fessor Viala  of  Montpellier  with  a  view  to  finding,  in  the  strongly 
calcareous  lands  of  Texas,  a  phylloxera-resistant  grapevine  which  would 
also  resist  chlorosis.  Viala  was  successful  in  this  quest,  and  the  stocks 
and  hybrids  obtained  from  the  Texas  vines  now  form  the  main  basis  of 
"reconstituted"  vineyards  in  France. 


Marly  or  excessively  limy  soils  are  quite  exceptional  in  California, 
so  much  so  that  until  quite  recently  only  one  case  of  chlorosis  resulting 
from  that  cause  had  come  to  the  knowledge  of  the  Station.  The  yel- 
lowing of  orange  and  lemon  leaves,  not 'uncommonly  observed  at  some 
points  in  southern  California,  has  throughout  been  due  to  other  defects 
in  the  subsoil,  which  weakened  the  root-growth  or  gave  rise  to  fungous 
di  sense. 

Citrus  orchards  in  the  Great  Valley  have  thus  far  been  remarkably 
free  from  some  of  the  troubles  noted  south  of  the  Tehachapi ;  the  chief 
complaints  having  been  caused  by  the  effects  of  water-seepage  from 
high  lying  ditches  in  the  foothills-  The  soils  themselves  have  not  been 
found  in  fault  except  where  it  was  attempted  to  plant  orchards  on 
heavy  clay  subsoils,  or  hardpan ;  emphasizing  the  need  of  a  careful 
examination  of  the  substrata  of  any  land  designed  for  tree  culture. 

Quite  lately,  however,  complaints  of  yellowing  and  languishing  of 
citrus  trees  grown  in  apparently  the  best  quality  of  loam  soil  in  the 
Porterville  region  have  come  to  the  Station.  Portions  of  young  orch- 
ards planted  on  low  ridgy  land  were  found  to  become  diseased,  their 
leaves  yellowing  and  dropping;  while  those  located  in  lower  ground 
continued  to  grow  thriftily.  The  samples  of  soil  and  subsoil  (the  latter 
taken  to  the  depth  of  from  3  to  5^  feet  in  accordance  with  the  direc- 
tions given  from  the  Station)  showed  that  while  in  the  lower  ground 
where  the  trees  were  in  good  condition,  the  subsoil  at  3  feet  contained 
only  12  per  cent,  of  lime  carbonate,  on  the  higher  land  it  was  full  of 
white  lime-nodules  in  the  third  foot ;  and  that  the  fine  earth  around 
them,  in  which  the  roots  vegetated,  contained  from  22  to  39  per  cent,  of 
lime  carbonate.  This  evidently  exceeds  the  tolerance  of  citrus  roots, 
hence  the  yellowing  of  the  leaves.  In  another  similar  case,  examination 
showed  that  even  where  the  trees  were  doing  finely  (the  soil  being  very 
rich),  the  calcareous  layer  was  reached  at  from  4^  to  5^  feet.  It  is 
probable  that  so  soon  as  with  progressive  growth  the  roots  reach  the 
above  depth  they  will  here  also  be  affected  by  the  excess  of  lime. 

This  is  a  condition  which  perhaps  cannot  be  remedied  by  any  appli- 
cations made  to  the  land.  When  lands  have  been  injured  by  artificial 
over-liming  or  excessive  marling,  the  effects  can  be  neutralized  by  the 
use  of  organic  matter,  usually  applied  in  the  form  of  stable  manure, 
a  procedure  already  prescribed  in  the  classic  treatise  on  Marling,  by 
Kuffin  of  Virginia,  early  in  the  last  century.  But  it  is  clearly  impos- 
sible to  apply  this  remedy  in  the  case  of  lands  naturally  underlaid  by 
marl ;  at  least  in  the  arid  region,  where  roots  penetrate  to  depths  un- 
known east  of  the  Mississippi.  No  vegetable  material  could  be  artifi- 
cially applied  at  depths  of  several  feet.  Inquiry  has  been  made 
whether  it  would  not  be  possible  to  neutralize  the  lime  by  some  acid ; 
but  this,  even  if  financially  possible,  would  surcharge  the  upper  layers 
with  a  substance  more  injurious  than  the  excess  of  lime  itself.  Pos- 
sibly an  antidote  may  be  found  in  some  soluble  compound  of  magnesia. 

Such  lands  should  simply  be  given  to  some  other  culture  than  citrus 
trees ;  and  among  these,  grapevines  on  their  own  roots,  or  upon  some  of 
the  lime-resistant  varieties  developed  in  France,  will  be  found  avail- 
able wherever  the  loose  soil  extends  to  4  or  5  feet  depth.     Other  cul- 


JW 


tures  resistant  to  marly  soils  are  the  fig,  stone  fruits  on  Myrobalau  or 
Chicka saw-plum  roots,  and  the  quince ;  also  most  legumes. 

It  should  be  kept  in  mind  that  calcareous  geological  formations 
extend  along  the  Sierra  foothills  from  the  Merced  Eiver  south  through 
Fresno  and  at  least  northern  Tulare  County,  and  can  be  observed  in 
the  bluffs  of  the  streams  as  they  emerge  from  the  foothills.  It  is  per- 
fectly easy  for  any  one  to  test  these  whitish  materials  for  lime,  and  to 
recognize  the  lime  hardpan  in  subsoils,  by  a  few  drops  of  muriatic  or 
nitric  acid,  or  even  strong  vinegar ;  which  will  cause  them  to  ' '  effer- 
vesce'' or  "fizz"  from  gas  bubbles  driven  off  by  the  acid.  A  bit  of 
chalk  or  limestone  can  be  used  for  comparison,  thus  gaining  some  idea 
of  the  liminess  of  the  material.  Long  low  ridges  extending  valley- 
ward  from  the  foothills  may  be  suspected  of  being  marly,  and  should 
be  examined  as  to  the  nature  of  their  subsoil  before  planting.  Entirely 
similar  conditions  exist  locally  in  portions  of  the  Santa  Clara  River 
Talley,  and  on  some  other  Coast  Range  streams  in  the  south.  Also  at 
a  few  points  in  the  Santa  Cruz  Range. 


The  matters  discussed  above  emphasize  from  an  additional  point  of 
view  the  need  of  subsoil  examination  in  the  arid  region  especially,  be- 
cause of  the  deep  rooting  01  all  plants  and  particularly  of  trees.  It 
seems  desirable  to  call  attention  to  another  and  very  obvious  mode  of 
recognizing  any  unusual  conditions  of  soil  and  subsoil,  viz.,  the  native 
vegetation.  I  have  elsewhere*  discussed  somewhat  elaborately  the  im- 
portance of  the  observation  of  native  growth  by  landseekers  and  farm- 
ers. It  may  be  said  in  brief  that  the  native  vegetation  is  ordinarily  the 
outcome  of  centuries  and  millennia  of  "natural  selection,"  which  re- 
sults in  the  predominance  of  the  species  of  plants  best  adapted  to  the 
surroundings  as  a  whole,  and  to  the  soil  in  particular.  Hence  such 
native  growth  must  be  presumed  to  express  the  same  facts  and  adapta- 
tions which  we  subsequently  find  out  laboriously  by  the  successes  and 
failures  of  various  crops.  What  we  need  is  to  be  able  to  interpret  cor- 
rectly the  indications  presented  to  us  by  the  native  growth. 

To  some  extent  this  has  been  and  is  daily  done  by  farmers  all  over 
the  world,  who  buy  wild  land  in  accordance  with  the  indications  of  the 
tree  growth  where  such  exists.  In  many  Eastern  States  the  official 
assessment  of  lands  is  habitually  based  upon  the  natural  tree-growth, 
and  the  judgment  of  experienced  men  on  this  basis  is  rarely  at  fault, 
and  has  even  excited  the  envy  of  agricultural  chemists. 

In  the  eastern  United  States  and  in  the  humid  region  generally,  the 
presence  or  absence  of  an  adequate  supply  of  lime  in  the  soil  is  largely 
the  determining  factor  of  the  vegetative  character;  more  so  even  than 
the  moisture  conditions,  which  are  commonly  credited  with  being  the 
chief  governing  condition. 

In  the  arid  regions,  where  lime  is  almost  universally  present  in 
soils  to  the  needful  and  useful  extent,  moisture  is  undoubtedly  the 

*  "Soils,"  MacMillan  Co.,  1906. 


dominant  factor  causing*  differences  in  native  vegetation.  We  are 
therefore  deprived  to  a  large  extent  of  the  signs  by  which  good  lands 
are  recognized  by  the  Eastern  settler,  the  more  as  forest  growth  is  not 
so  abundant  in  the  arid  region.  We  must,  in  order  to  utilize  the  indi- 
cations of  the  soil-character  by  native  vegetation,  observe  not  merely 
the  kinds  and  development  of  trees  on  the  ground,  but  also  the  shrubby 
and  herbaceous  growth ;  noting  not  only  the  presence  but  also  the  ab- 
sence of  plants  prevailing  in  the  neighborhood,  from  certain  portions 
of  the  area. 

Every  one  in  California  knows  the  "alkali  weeds,"  which  tell  him 
that  the  land  on  which  they  grow  is  more  or  less  impregnated  with 
salts ;  many  have  even  now  learned  which  of  these  plants  indicate  land 
which  under  present  conditions  it  will  not  pay  to  try  to  reclaim.  Now 
just  as  some  plants  will  resist  a  greater  or  less  amount  of  alkali  salts 
than  others,  so  some  plants  are  tolerant  of  an  excess  of  lime  in  the  soil, 
while  others  will  refuse  to  grow,  or  at  least  will  not  naturally  be  found 
occupying,  ground  containing  more  than  the  limited  amount  of  lime, 
which  is  in  all  cases  desirable. 

The  infrequent  occurrence  of  marly  lands  in  California,  already 
referred  to,  has  been  the  cause  of  the  fewness  of  observations  made  in 
regard  to  the  distinctive  natural  vegetation  of  such  tracts.  It  is  evi- 
dently very  desirable  that  such  observations  should  be  made  for  the 
benefit  of  future  planters  of  orange  orchards ;  and  the  marly  ridges  of 
the  Porterville  region  afford  a  good  opportunity  for  this  purpose. 
Undoubtedly  some  of  the  shrubs  and  herbaceous  plants  prevailing  else- 
where in  that  region  will  be  found  wanting  on  the  marly  ridges  or  belts. 
Among  these  will  doubtless  be  the  Lupins,  which  are  very  prevalent 
in  the  foothill  and  plains  region  of  Fresno  and  Merced.  Lupins  re- 
quire about  one-half  of  1  per  cent,  of  lime,  and  some  will  resist  as 
much  as  2  per  cent. ;  but  marly  soils  such  as  those  referred  to  above 
will  certainly  not  bear  any  native  Lupins.  I  doubt  that  even  the  gray 
sage  will  grow  on  land  thus  heavily  impregnated.  That,  however,  is  a 
question  of  fact  which  those  living  on  the  spot  should  readily  deter- 
mine. If  any  such  will  send  samples  of  the  plants  naturally  growing 
on  such  lands  to  the  Station,  they  would  aid  in  the  settlement  of  these 
questions. 


